The features of the method of and system for measuring the temperature and spectral factors are (1) that no preliminary data concerning the spectral factors in accordance with the invention of the specimen is required, (2) that the temperature and spectral factor (involving both value and color) can be measured at the same time, (3) that it is thus not necessary to regard the spectral factor as a function of temperature although actually it is a function of wavelength and temperature, (4) that the aforementioned one-dimensional equation for obtaining the temperature would not become complicated even if the number of channels were to be increased, and (5) that while when analyzing the radiant flux into M channels the spectral flavor expressed as a function of wavelength should be represented as having M.times.N possible values, which would give an exact value of spectral factor with respect to the overall specimens, because the spectral factor of each specimen has M possible values respectively (i.e. if the spectral factor .epsilon..sub.i for an i-th channel with respect to the n-th specimen can be .epsilon..sub.n1, .epsilon..sub. n2, . . . , .epsilon..sub.nM for the M analyzed channels), the possible value of the spectral factor is approximated into M-N (N=1 in the case of only one specimen), however no approximation is involved in the deduction process of the equation. Therefore, the accuracy of the solution of the one-dimensional equation, (i.e. value measured) is high.
The spectral factors which are dealt with in the invention include not only the spectral emittance but also spectral reflectance and spectral transmittance which are values representing physical properties of the specimen, other factors such as those representing the surface roughness, shape and area of the specimen, positional relation between the specimen and measuring instrument, state of light path between the specimen and measuring instrument, etc. Further, a composite factor regarding the combination of the emittance, reflectance and transmittance may be included. There is no relation between the emittance .epsilon. and reflectance .rho., and the invention can be applied to the case even where .epsilon.+.rho..noteq.1.
Now, the comparison between a prior-art system and the system according to the invention will be made in connection with the case of measuring the temperature and spectral factor by spectrally analyzing the radiant flux from a single specimen (N=1) into several channels without using preliminary data concerning the spectral factor.
(a) One-channel measuring system: This system corresponds to the prior-art brightness temperature measurement. With this system, there is no freedom for the measurement of the spectral factor, so that it can be adopted only where the specimen is a blackbody. According to the invention, this system is avoided.
(b) Two-channel measuring system: This system corresponds to the prior-art distributed temperature measurement. With this system, the freedom for measuring the spectral factor is 1, and the extent of gray of the specimen (i.e., value-wise character) can be obtained. In other words, when expressing spectral factor as a function of the wavelength, the spectral factor is obtained as a constant term in the function. This system is not adopted according to the invention. In contrast, according to the invention, a method is employed in which a plurality of combinations of two channels are produced by appropriately selecting two of three or more spectral radiant flux channels, the temperature and gray spectral factor are obtained for each of the two-channel combinations by using a two-channel measuring system (based upon the principles of the two-color spectrophotometric pyrometer), and the gray factor is corrected to a color-including spectral factor such that an equal temperature is obtained for all of the two-channel combinations, which system is dissimilar to the two-channel measuring system.
(c) Three-channel measuring system: This system has not hitherto been proposed, that is, it is first adopted according to the invention. In this system, there are two possibilities for the measurement of the spectral factor, and the extent of gray of the specimen and way of presentation of color (i.e., a character resembling the value and hue) are obtained. For example, when expressing the spectral factor as a high-degree polynomial of wavelength, the constant term (factor of zero-degree term) and factor of the first-degree term can be obtained.
(d) M-channel (M.gtoreq.3) measuring system: In this system, there are M-1 possibilities for the measurement of the spectral factor, and the extent of gray of the specimen, way of presentation of color and extent of partialness of color (a character resembling the value, hue and chroma) can be obtained. For example, the spectral factor can be expressed as an (M-2)-th degree polynomial of the wavelength.